1. Field of the Invention
The present disclosure relates to an image forming apparatus that transfers a developer image formed on a photosensitive member to a recording medium.
2. Description of the Related Art
As image forming apparatuses, there are provided apparatuses that form an electrostatic latent image on a photosensitive member and develop the formed electrostatic latent image using a developing unit including a developing roller, thereby forming a visible image. If the developing roller and the photosensitive member are left in the state of being in contact with each other for a prolonged time, both the developing roller and the photosensitive member will locally deform, which may cause a defect image. Furthermore, if the developing roller and the photosensitive member that are in the state of being in contact with each other are rotated more than needed, the photosensitive member will wear due to friction between the developing roller and the photosensitive member, and the lifespan of the photosensitive member will be reduced. Accordingly, Japanese Patent Laid-Open No. 2006-292868 discloses an image forming apparatus that is configured to perform operations for bringing the developing roller into contact with and separating the developing roller from the photosensitive member, thereby reducing the amount of time during which a photosensitive member and a developing roller are in contact with each other.
Furthermore, as disclosed in Japanese Patent Laid-Open No. 09-230259, there is provided an image forming apparatus in which a scanner motor rotates a polygon mirror in order to scan a photosensitive member. Since the scanner motor has a high inertia and it takes a long time until the scanner motor stably rotates, it is necessary to start driving the scanner motor simultaneously with a printing instruction. Furthermore, in order for a light-receiving sensor to detect the rotating speed of the scanner motor, a semiconductor laser is turned on. When the rotating speed of the scanner motor becomes stable at a target rotating speed, turning on and off of the semiconductor laser is performed in accordance with synchronization signals input in the light-receiving sensor, preventing the photosensitive member from being irradiated with light (referred to as unblanking light emission).
As describe in Japanese Patent Laid-Open No. 2006-292868, the developing roller is separated from the photosensitive member while no image forming processing is being executed, and the developing roller is brought into contact with the photosensitive member at the start of the image forming processing. When the scanner motor starts rotating at the start of the image forming processing, the light source emits light for the detection of the rotating speed of the scanner motor. During this light emission, the photosensitive member is exposed to the light. Accordingly, if the developing roller and the photosensitive member come into contact with each other during the light emission, developer adheres to the exposed position of the photosensitive member. The developer adhering to the photosensitive member will eventually adhere to the rear face of a recording material and, in other words, cause marking on the back of the material. Therefore, it is necessary to start control of the developing roller such that the developing roller comes into contact with the photosensitive member after the rotating speed of the scanner motor becomes stable and the light source is shifted to unblanking light emission.
Consequently, it takes a long time from the start of the image forming processing until when the developing roller is brought into contact with the photosensitive member, that is, from the start of the image forming processing until it is possible to form a developer image.